Drilling an oil and gas well with a conventional rotary drilling rig requires an elevator and a spider arranged in alignment with an opening in the rig rotary table are used in tandem to add and remove segments or joints of threaded tubing pipe, such as drill pipe or casing pipe, to the long strings of pipe placed in the wellbore. The spider is mounted within or over the rotary table of the drilling rig and the elevator is suspended above the spider on the hangers by bails attached to a hoist mounted on the drilling rig. The elevator and spider in combination are used to lift, hold, and release the pipe segments.
The pipe segments have collars that extend radially around the pipe periphery that with internal connecting threads used to connect the pipe segments together to form the pipe string. The collars have annular surface called a shoulder at the base of the radially collar. Elevators that support the pipe string on this shoulder are called shoulder elevator. Shoulder elevators often support pipe strings that weigh hundreds of tons and that great weight puts substantial stress, strain, and fatigue on the elevator and its components during use.
Shoulder elevators often have a static open ring used for receiving the tubular and supporting the tubular on the collar. Often these open rings have a door or doors that close around the tubular. Some elevators employ pivoting jaws where the elevator hangers are supported on bails that are suspended from a hoist. The jaws and hangers cause these elevators to cant or tilt even when no loads are being support or when the jaws are being opened to release a tubular.
Current shoulder elevators have many shortcomings that often lead to an eccentrically supported tubular that gives a pronounced cant or tilt to the elevator and the tubular being lifted. The elevator doors of shoulder elevators are prone to failure because of inadequate door design or because the elevator does not provide complete contact and support around the full circumference of the tubular collar. Elevators with hangers on pivoting jaws pivot on the hangers and move outwardly as the jaws are opened to receive a pipe. The outward movement shifts the center of gravity of the elevator causing the elevator jaws to sag when not attached to a pipe and require additional effort to level the elevator when receiving a pipe. A tubular collar not fully supported increases the likelihood of eccentric loading and the likelihood that the tubular will be shifted towards the ring opening or door. This shifting increases the risk of door failure and limits the maximum load which the elevator can safely handle. Any elevator failure will suspend drilling operations and may cause a lost or dropped pipe creating a significant risk property damage and personal injury.
Current elevators also suffer from lack of versatility as they are often sized for pipe having a specific diameter. Typically different elevators must be used when drilling operation require a change in tubular diameters, such as when a change is made between casing sizes. The lack of versatility requires drilling companies to maintain differently sized elevators on site and increases rig time and the drilling cost.